Annular circuit components coupled with printed circuit board through-hole

ABSTRACT

A circuit component assembly and a method for forming the assembly as an annular body in a laminate, preferably between a trough-hole or via and a surrounding conductive layer in a PCB are disclosed, the circuit component assembly including one or more resistors/conductors, inductors and dielectrics/capacitors or combinations thereof, outer and inner peripheries of the circuit component preferably having substantially constant radii permitting simple determination of operative electrical characteristics for the circuit component from (a) the inner and outer radii, (b) an effective thickness for the circuit component and (c) its electrical characteristics determined by the material formed in the annular recess, the circuit component body preferably being formed from a liquid precursor forming conductive interconnections for the circuit component assembly at its outer and inner perimeters.

This is a continuation-in-part of U.S. patent application Ser. No.08/044,301 filed Apr. 7, 1993, U.S. Pat. No. 5,347,258, under assignmentto the assignee of the present invention.

FIELD OF THE INVENTION

The present invention relates to printed circuit boards and moreparticularly to printed circuit boards including various devices orcomponents to be coupled with individual passive circuit components suchas resistor/conductors, inductors or dielectric/capacitors and compoundcircuit components (networks) formed from combinations of passivecircuit component.

BACKGROUND OF THE INVENTION

The present invention is directed toward printed circuit boards (PCBs)and the like. These circuit boards typically include large numbers ofelectronic devices which are commonly surface mounted and alsoadditional component which may be present in the form of active layerswithin or on each PCB. The requirement for the devices and components insuch printed circuit boards are subject to conventional electronicdesign restraints.

More specifically, many of the surface mounted devices and othercomponents on such PCBs commonly require coupling with individualpassive circuit components such as resistor/conductors, inductors ordielectric/capacitors in order to achieve their desired function.

The solution to this problem in the prior art has been the use ofindividual discrete passive components commonly surface mounted on thePCBs. PCB design has further required the provision of though-holes inorder to properly interconnect the passive circuit components. In thisregard, the passive circuit components may be interconnected between anycombination of surface devices or component, active circuit componentsor layers formed on or within the PCBs.

Accordingly, the provision of such discrete or individual passivecircuit components has increased the complexity of the PCBs and at thesame time either decreased the available surface area of the PCBs forother devices or else resulted in an overall increase in the size of thePCBs to accommodate necessary surface devices and components includingpassive circuit components.

A more recent solution to this problem in regard to resistive circuitcomponents in the prior art has been the provision of planar components,typically resistors, preferably formed on layers of the PCBs to replaceprior art surface mounted resistors as described above, thus makingsurface portions of the PCBs free for other uses.

Although such planar resistors provide advantages in certainapplications over discrete surface mounted resistors, they have stilltended to result in relative increases in the complexity and spacedemands on the PCBs. For example, if the planar resistors are formed ona surface layer of the PCB, it is of course possible to arrange anactive surface device over the resistor. However, that surface portionof the PCB occupied by the planar resistor must be dedicated to theplanar resistor itself. Accordingly, that portion of the board is notavailable for mounting pads, through-holes or the like. At the sametime, it is also necessary to provide conductive couplings forinterconnecting the surface formed planar resistors in order couple themwith active devices or components in the PCBs. Here again, platedthrough-holes have commonly been employed for this purpose and furtherincrease complexity and space demands in the PCBs.

Planar resistors of the type described above have also been formed oninternal layers or planes of the PCBs. Such a configuration permits theuse of standard subtractive PCB techniques, for example, to produceconductor patterns and resistor elements suited for high speed and highdensity circuit applications. However, even with planar resistors formedon internal layers of the PCBs, it is still necessary to provide platedthrough-holes or other conductors extending in a Z direction through thePCBs in order to provide the necessary couplings for the planarresistors with various surface mounted devices or components in thePCBs.

Thus, there has been found to remain a further need for improvements inthe provision of passive circuit components and compound circuitcomponents formed by combinations of passive circuit components for usein PCBs.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide animproved design for PCBs and the like including circuit components onexternal surfaces or internal layers of the PCBs.

It is particularly contemplated in connection with the present inventionthat the circuit components be formed from generally conventionalmaterials exhibiting desired characteristics.

The circuit components may include, for example, resistors/conductors,inductors, dielectrics/capacitors, combinations of the above andpossibly additional components as well. Within the scope of the presentinvention, it is to be noted that all resistors necessarily exhibitconductance and similarly all conductors necessarily exhibit someresistance. Accordingly, resistors and conductors are considered as agenerally constant spectrum dependent only upon the specific resistanceand conductance of the component of the component. Similarly, adielectric component may function as a true dielectric or isolatingcomponent or as a capacitor depending upon the specific dielectricconstant for the component. Accordingly, dielectrics and capacitors arealso considered as a generally continuous spectrum in the presentinvention depending upon the specific dielectric constant.

However, it is a more particular object of the invention to form thecircuit components of the present invention in combination withthrough-holes in the PCB.

The term "circuit board" is employed herein to include printed circuitboards and other device substrates such as integrated devices,multi-chip modules and similar devices having signal traces on differentlayers.

The term "through-hole" is employed herein to refer to any Z directionalconductor formed in the PCB for interconnecting a surface device or PCBcomponent with a conductive layer on or in the PCB. For example,through-holes are commonly employed for interconnecting surface mounteddevices on the PCB either with an internal conductive layer or planewithin the PCB or even a surface conductive layer on the PCB. In thelatter case, the most common arrangement would be a through-holeinterconnecting a surface device on one side of the PCB with aconductive layer or plane on the opposite surface of the PCB. At thesame time, through-holes of the type defined above are also employed forinterconnecting surface mounted devices or components arranged on or inthe PCB with conductive layers or planes formed either on or in the PCB.Accordingly, the present invention preferably contemplates formation ofits circuit component or components in combination with through-holes asdefined above. The through-hole described above may also be replaced bya central conductor, the central conductor thus serving as a means forcompleting a circuit including the circuit component assembly of thepresent invention and the surrounding conductive layer.

More specifically, it is an object of the invention to provide aresistor/conductor assembly in a PCB, the assembly including aconductive through-hole formed in the PCB for interconnection with asurface device or other PCB component, a conductive pad surrounding andconductively interconnected with the plated through-hole, a conductivelayer surrounding and generally coplanar with the conductive pad andspaced apart from the conductive pad to form an annular recess, aresistor/conductor assembly being arranged in the annular recess andformed from a conductive material having a selected resistivity andouter and inner perimeters respectively conductively interconnected withthe conductive layer and the conductive pad whereby theresistor/conductor assembly is electrically coupled along with theplated through-hole between the conductive layer and the surface deviceor component.

Broadly, the present invention contemplates such a resistor/conductor orresistor/conductor assembly wherein the annular recess forms acontinuous channel or separation between the conductive layer and theconductive pad or plated through-hole. At the same time, theresistor/conductor assembly is arranged in the annular recess and ispreferably at least co-extensive with the annular recess. In such aco-extensive arrangement, the resistor/conductor assembly either extendsjust between the outer and inner perimeters or may even overlap theouter and inner perimeters as described in greater detail below.

It is a further related object of the invention to provide such aresistor/conductor assembly wherein the outer and inner perimeters ofthe resistor/conductor assembly are each formed with a substantiallyconstant radius with the resistor/conductor assembly being at leastgenerally coextensive with the annular recess whereby the operativeresistance of the resistor/conductor assembly may be simply determinedfrom the radii of its outer and inner perimeters, and effectivethickness, of the assembly and its resistivity. It is even morepreferably contemplated that the conductive layer and conductive padhave generally equal thicknesses at their respective interconnectionswith the resistor/conductor assembly for establishing the effectivethickness of the assembly. In this case, the resistor/conductor assemblyis assumed to have a thickness approximately equal to those of theconductive layer and conductive pad.

Within such a configuration, the resistor/conductor assembly may readilybe formed, for example, by deposition of a liquid precursor or by othermethods of formation which will be apparent from the followingdescription.

It is more broadly an object of the invention to provide such aresistor/conductor assembly at the juncture of a plated through-hole ina PCB with a surrounding conductive layer, the assembly having an outerperimeter conductively interconnected directly with the conductive layerand an inner perimeter conductively interconnected with the platedthrough-hole. Here again, the outer and inner perimeters of theresistor/conductor assembly are preferably formed with substantiallyconstant radii so that the operative resistance of the assembly may besimply determined from the radii of its outer and inner perimeters, aneffective thickness of the resistor assembly and its resistivity.

It is further contemplated in connection with the objects set forthabove that the operative resistance of the resistor orresistor/conductor assembly be capable of estimation in the mannersummarized above. More specifically, a typical method for estimating theoperative resistance of the resistor/conductor is set forth immediatelybelow.

At least in a preferred embodiment of the present invention with theouter and inner peripheries of the resistor/conductor assembly havingconstant radii, the effective resistance of the assembly may bedetermined as follows, having reference to FIG. 5B.

If R equals resistance, then it may be calculated as ##EQU1## where Requals resistance in ohms, p equals resistivity of the resistor in ohmscentimeters, L equals the length of the resistor in centimeters, wequals the width of the resistor in centimeters and H equals the heightof the resistor in centimeters (wH thus being the effectivecross-sectional area of the resistor for purposes of calculating itsresistance).

Referring briefly to FIG. 5B, as described below, the resistor body 62is graphically illustrated with substantially constant radii forming itsouter and inner peripheries 56 and 58. Further, since the resistor body62 forms a resistor between the conductive pad 60 and the conductivelayer or upper surface 22, then the effective length of the resistorbody 62 is equal to the radial dimension of the resistor body, that isr₂ -r₁. The effective width of the resistor body is thus the meancircumference of the resistor body, that is the circumference of theresistor body generated from a point mid-way between the outer and innerperipheries 56 and 58. Thus, the effective width of the resistor bodymay be stated as follows: ##EQU2##

These effective values for length and width may then be substituted intothe basic equation set forth above for resistance. It may readily beseen from FIG. 5B that the overall resistance of the resistor body willbe proportional to the differential radius, that is r₂ -r₁. At the sametime, resistance is inversely proportional to the effective width of theresistor body as stated above.

The above equations can readily be employed for adjusting the radii ofthe outer and inner peripheries of the resistor body in order to provideany desired resistance, at least given the effective height (H) for theresistor body. It is also possible of course to permit variation of theeffective height of the resistor body for purposes of determiningoverall resistance.

The equations set forth above thus readily facilitate the calculation ofresistance relative to dimensions for a preferred embodiment of theresistor body as illustrated in FIG. 5B. At the same time, variations inthe configuration of the resistor body may similarly be included in suchmathematical determinations, but possibly with increased complexityrelative to the equations set forth above.

The summary includes numerical labels described in greater detail belowbut set forth here for the purpose of facilitating application of thesummarized equations with the preferred embodiments described below.

In a preferred embodiment of the present invention with the outer andinner peripheries of the resistor or resistor assembly having constantradii, the effective resistance of an annular resistor orresistor/conductor assembly may be more precisely determined as follows,having continued reference to FIGS. 5B and 5D.

Generally, the macroscopic quantities voltage (V), current (i), andresistance (R) apply to a particular body or extended shape. Themacroscopic quantities are determined from the corresponding microscopicvector quantities (point quantities) electric field (E), current density(j), and scalar quantity resistivity (ρ). The microscopic quantities areexpressed as,

    E=ρj                                                   (1)

and the corresponding macroscopic quantities are expressed as,

    V=iR                                                       (2)

The resistance of a material between points a and b (of any materialshape) can be expressed in microscopic tens by the followingrelationship, ##EQU3##

In this expression, the line integral d1 defines the line ab along thepath E, and a closed loop path is defined by the surface integral dS,which corresponds to the area enclosed by a current i.

The above microscopic expression applied to a rectangular resistor bodywith dimensions (h, w, l), as shown in FIG. 5D, upon integration,readily yields the macroscopic quantity which states that the resistanceof a rectangular resistor body is directly proportional to its lengthand indirectly proportional to its cross-sectional area, ##EQU4## Theerror analysis for this relationship (regarding the rectangulargeometry) is straight forward and is expressed as, ##EQU5##

A model of an annular resistor is shown in FIG. 5B. The model has beensimplified in that the resistor body does not overlap the top of theconductor plane. Overlapping the conductor plane reduces the resistanceof the resistor per unit volume by exposing more resistor contact areato the copper foil. If overlap cannot be avoided, the expression can bemodified to account for overlap as shown by equation (7) below.

Referring to FIG. 5B, an annular resistor body 62 is graphicallyillustrated with substantially constant radii forming its outer andinner peripheries 56 and 58. The resistance value of the annulargeometry can only be approximated and is not accurately described by theabove expression relating to the rectangular resistor geometry. Thecross-sectional area of the annular resistor is a continuously andsmoothly changing function of the radii. This functionality is describedby the logarithmic ratio of the outer to inner diameter. Assuming thatthe radial symmetry between the inner contact pad 60 and the annularresistor body 62 is controlled and maintained during processing, then,the resistance of the annular resistor geometry is exactly expressed as:##EQU6##

Further, if overlap cannot be avoided, the above expression can bemodified as follows: ##EQU7##

In this expression, d₂ /d₁ describes the ratio of the outer to innerdiameters.

The error function for the annular geometry equation for resistance isgiven by: ##EQU8##

The above equations can readily be employed for adjusting the radii ofthe outer and inner peripheries of the annular resistor body in order toprovide a desired resistance, at least given the effective height (h)for the resistor body. It is also possible of course to permit variationof the effective height of the resistor body for purposes of determiningoverall resistance.

The equations set forth above thus readily facilitate the exactcalculation of resistance relative to dimensions for a preferredembodiment of the resistor body as illustrated in FIG. 5B. The functionR(ρ,h,d₁,d₂) and likewise the error function of R have four dependentvariables, with the dependency of those variables relating to processingconditions such as control over ring thickness, ring dimensions andplanarization. In the annular geometry of the preferred embodiment, thelogarithmic function (of the cross-sectional area of the annulus)controls the resistive value of resistor body. In order to visualizeresistance tolerance of a processed annular ring resistor, a plot of theerror function equation (8) against the ratio of the outer to innerdiameters is illustrated in FIG. 13. In order to provide an example ofwhat can be expected from the resistive tolerance of the annular ringgeometry, the parameters and tolerances chosen for this evaluation areas follows: d1=20±1.0 mil., d2=20 to 68±1.0 mil., h=1.25±0.25 mil andρ=1000±100Ωmil. These particular parameters and tolerances were chosenfor purpose of example only, and are not intended to be limiting in thepresent invention.

By consideration of a permutation of the tolerance examples of the fourvariables, the above figure defines an envelope for the tolerance rangeof R. The tolerance range is bounded to all values inside this envelope.The tolerance envelope of FIG. 13 illustrates that the annular resistortolerance is dominated by the logarithmic dependence of the radii (thelog function relating to the cross-sectional area of de annulus), thatlogarithmic function being non-linear. However, FIG. 13 indicates thatthe tolerance range does generally increase, allowing better tolerancecontrol in processing when the annular geometry is taken intoconsideration. In this regard, the error function indicates that theouter ring diameter should be not more than 2 times the inner diameterin order to keep the resistance tolerance low (<20%).

It is further contemplated by the present invention to provide inductorcomponents of simplified design with reduced surface requirements.

It is particularly contemplated in connection with the present inventionthat the inductor components be formed from generally conventionalmaterials such as iron ferrite disposed in a matrix structure to providea selected inductance. Accordingly, the inductance of each inductorcomponent of the present invention is determined by its dimensions andthe permeability of the ferromagnetic material.

Just as with the resistor element of the present invention, it is a moreparticular object of the invention to provide a simplified design forthe inductor components while reducing surface requirements within thePCB by forming the inductor components in combination with through-holesin the PCBs for interconnecting surface devices or components withconductive layers on or in the PCB.

More specifically, it is an object of the invention to provide aninductor assembly in a PCB, the assembly including a conductivethrough-hole formed in the PCB for interconnection with a surface deviceor other PCB component, a conductive pad surrounding and conductivelyinterconnected with the plated through-hole, a conductive layersurrounding and generally coplanar with the conductive pad and spacedapart from the conductive pad to form an annular recess, an inductorassembly being arranged in the annular recess and formed fromferromagnetic material having a selected inductance and outer and innerperimeters respectively conductively interconnected with the conductivelayer and the conductive pad whereby the inductive assembly iselectrically coupled along with the plated through-hole between theconductive layer and the surface device or component.

Broadly, the present invention contemplates such an inductor or inductorassembly wherein the annular recess forms a continuous channel orseparation between the conductive layer and the conductive pad or platedthrough-hole. At the same time, the inductor assembly is arranged in theannular recess and is preferably at least co-extensive with the annularrecess. In such a co-extensive arrangement, the inductor assembly eitherextends just between the outer and inner perimeters or may overlap theouter and inner perimeters due to processing restraints.

It is a further related object of the invention to provide an annularinductor assembly wherein the outer and inner perimeters of the annularinductor assembly are each formed with a substantially constant radiuswith the annular inductor assembly being at least generally coextensivewith the annular recess whereby the operative inductance of the annularinductor assembly per unit length to may be simply determined from thecross sectional area of the inductor assembly, the effective thicknessof the inductor assembly and its permeability. It is even morepreferably contemplated that the conductive layer and conductive padhave generally equal thicknesses at their respective interconnectionswith the annular inductor assembly for establishing the effectivethickness of the inductor assembly. In this case, the annular inductorassembly is assumed to have a thickness approximately equal to those ofthe conductive layer and conductive pad.

Within such a configuration, the annular inductor assembly may readilybe formed, for example, by deposition of a liquid precursor or by othermethods of formation which will be apparent from the followingdescription.

It is more broadly an object of the invention to provide such an annularinductor assembly at the juncture of a plated through-hole in a PCB witha surrounding conductive layer, the annular inductor assembly having anouter perimeter conductively interconnected directly with the conductivelayer and an inner perimeter conductively interconnected with the platedthrough-hole. Here again, the outer and inner perimeters of the inductorassembly are preferably formed with substantially constant radii and theinductor is generally continuous between its outer and inner perimetersforming an annular ring structure. It is further contemplated inconnection with the objects set forth above that the operativeinductance of the inductor or inductor assembly be capable ofcalculation in the manner summarized above. More specifically, a typicaland preferred method for calculating the operative inductance of theannular inductor or inductor assembly is set forth immediately below.

In a preferred embodiment of the present invention with the outer andinner peripheries of the annular inductor or inductor assembly havingconstant radii, the effective inductance may be determined as follows,having reference to FIG. 5B.

In FIG. 5B, an annular body is graphically illustrated withsubstantially constant radii forming its outer and inner peripheries. Aswith the annular resistor of the present invention, the cross-sectionalarea of the annular inductor is a continuously and smoothly changingfunction of the radii. This functionality is described by thelogarithmic ratio of the outer to inner diameters. Assuming that theradial symmetry between the inner contact pad and the annular inductorbody is controlled and maintained during processing, then the functionalrelationship for the annular inductor body may be expressed by thefollowing:

Let:

μ=permeability (H m⁻¹) of the ferromagnetic core

h=thickness of the ferromagnetic core

and the inductance (L) per unit length for an annular core inductorhaving an inner radius of r₁ and an outer radius of r₂ may be determinedin the following manner: ##EQU9##

The above equation can readily be employed for adjusting the radii ofthe outer and inner peripheries of the annular inductor body in order toprovide a desired inductance, at least given the effective height (h)for the inductor body. It is also possible of course to permit variationof the effective height of the inductor body for purposes of determiningoverall inductance.

The equation set forth above thus readily facilitates the calculation ofinductance relative to dimensions for a preferred embodiment of theinductor body with the same structure as that illustrated for theannular resistor body in FIG. 5B. At the same time, variations in theconfiguration of the inductor body may similarly be included in themathematical determination, but possibly with increased complexityrelative to the equation set forth above.

It is additionally contemplated by the present invention to providedielectric/capacitor components of simplified design with reducedsurface requirements in the same manner as discussed above in regard tothe resistor and inductor components.

It is particularly contemplated in connection with the present inventionthat the dielectric/capacitor components be formed from generallyconventional dielectric materials such as epoxies or resins (i.e.cyanate esters, polyimides and kapton materials) or other knowndielectric materials such as ceramic particles or powders in a suitablematrix to provide a selected capacitance. Accordingly, the capacitanceof each dielectric/capacitor component of the present invention isdetermined by the dielectric constant or relative permitivity of thedielectric material and its dimensions.

The dielectric/capacitor components of the present invention arecontemplated to be provided for in a PCB in the stone manner as for theresistor and inductor components discussed above, with a preferredembodiment having an annular ring structure formed in the same manner asthe aforementioned components. In this regard, the dielectric/capacitorcomponent is formed by a dielectric material disposed between theconductive layer and the conductive pad or through-hole. As with theresistor and inductor components of the present invention, the effectivethickness of the dielectric/capacitor assembly may be established by thethicknesses of the conductive layer and conductive pad. Similarly, theeffective capacitance may be determined in a generally similar manner asdescribed above for resistance and inductance.

In this regard, the capacitance (C) per unit length for an annularcapacitor assembly of the present invention formed with substantiallyconstant radii and having an inner radius of r₁, an outer radius of r₂,and an effective thickness (h) may be determined by the followingequation: ##EQU10## ε being defined as follows: ##EQU11## where ε_(r) isthe relative permutivity of the annular medium.

The above equation allows for the determination of the effectivecapacitance for a preferred embodiment of the annular capacitor assemblywhere r₁ and r₂ are substantially constant, but could be adapted forapplication to additional annular capacitor bodies where r₁ and r₂ arenot constant.

It is further contemplated by the present invention that the circuitcomponents may be employed to provide network circuit components such ashigh pass and low pass LC or RC (inductor-capacitor orresistor-capacitor) networks, pi-filter circuit networks and band passcircuit networks all comprising operative combinations of the passivecircuit components of the present invention. The term "filter" refersherein to circuit components allowing certain selected frequency signalsto pass through the circuit while blocking certain other frequencysignals.

In this regard, at least portions of such network circuits of thepresent invention may be formed within an annular recess in internal orexternal layers of a PCB where an annular passive circuit component isarranged within a different annular circuit component to form a seriesof operatively interconnected concentric circuit component bodies asillustrated in FIG. 8 and described in greater detail below. Here, theterm concentric is employed to mean a plurality of circuit componentbodies having a common axis where those bodies may be of a variety ofgeometric shapes.

It is yet a further object of the invention to provide a method offorming a passive circuit component or circuit component assembly asdefined above wherein an annular recess is formed in a conductive layerof a PCB, a circuit component assembly being formed in the annularrecess from a selected material with its outer perimeter conductivelyinterconnected with the conductive layer, a through-hole being formed inthe PCB and plated with conductive material conductively interconnectedwith an inner perimeter of the passive circuit component assembly. Theorder in which the steps are performed may be changed. For example, thethrough-hole could be formed prior to deposition of the circuitcomponent assembly in the annular recess. Here again, a conductive padcould also be formed about the plated through-hole for interconnectionwith the circuit component assembly.

It is a related object of the present invention to provide a method offorming an annular circuit component or component assembly by screeningmaterial into an annulus formed in a conductive layer of a PCB to forman annular resistor/conductor, inductor or dielectric/capacitor asdisclosed by the present invention.

It is a further related object of the present invention to provide amulti-pass sequential process for screening materials into an annulusformed in a conductive layer in a PCB to create a series of conductivelyinterconnected concentric annular circuit components in order to form acompound circuit according to the present invention.

It is also a further related object of the invention to provide aprocess as described above wherein the passive circuit component orcircuit component assembly includes multiple components, preferablyconcentrically formed in the annular recess.

Additional objects and advantages of the invention are made apparent inthe following description having reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a printed circuit board (PCB) with surfacedevices schematically illustrated for interconnection with variouscomponents of the PCB by respective through-holes.

FIGS. 2, 3 and 4 are respectively view taken in section along sectionlines II--II, III--III and IV--IV of FIG. 1.

FIG. 5A is a plan view of a capacitive laminate formed as a subassemblyfor inclusion in the PCB of FIG. 1 and illustrating, in greater detail,a resistor assembly formed according to the invention.

FIG. 5B is a fragmentary view of a single resistor body constructedaccording to the present invention and having a preferred configurationas also illustrated in FIG. 5A.

FIG. 5C is a view similar to FIG. 6 while illustrating the annularresistor formed on an internal layer of the PCB.

FIG. 5D illustrates a rectangular resistor body having dimensions (h, w,l).

FIG. 6 is a fragmentary view taken along section lines VI--VI of FIG.5A.

FIG. 7 is a fragmentary view illustrating a portion of a capacitivelaminate similar to that illustrated in FIG. 5A to demonstrate anotherembodiment of the invention.

FIG. 8 is a plan view of a similar annular circuit component havingconcentric rings with different electrical characteristics.

FIGS. 9A and 9B are schematic representations of high pass filterassemblies respectively including an inductor and capacitor or aresistor and capacitor.

FIGS. 10A and 10B are similarly schematic representations of low passfilters respectively including a capacitor and inductor or a capacitorand resistor.

FIGS. 11A and 11B are schematic representations of pi filters bothincluding parallel capacitors coupled respectively with either aninductor or resistor.

FIGS. 12A and 12B are schematic representations of bandpass filtersformed respectively from a parallel arrangement of an inductor andcapacitor coupled with a resistor or a capacitor and inductor coupled inseries with each other and with a resistor as illustrated.

FIG. 13 is a graphical representation of a resistor tolerance envelopefor an annular ring resistor.

FIGS. 14-20, taken together, provide a representation of sequentialprocessing steps for forming an annular resistor or circuit componentassembly according to the present invention.

FIGS. 17A, 18A, 17B and 18B, taken together, represent an alternative tothe method of FIGS. 14-20 and are adapted for forming an annular circuitcomponent having different concentric elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and particularly to FIGS. 1-4, a printedcircuit board (PCB) is generally indicated at 10 conventionally formedwith multiple layers as described in greater detail below with referenceto FIGS. 2-4. Surface mounted devices 12.14 and 16 are arranged upon anupper surface 18 of the PCB for interconnection with conductive layerswithin the PCB as described in greater detail below.

Referring to FIGS. 2-4, the internal layers of the PCB include acapacitive laminate 20 formed from conductive foils or layers 22 and 24arranged on opposite sides of a dielectric layer 26 formed for examplefrom epoxy or from other materials having a higher dielectric constant.The conductive foil 22 is a power plane for the PCB 10 while the otherconductive foil 24 is a ground plane for the PCB. Such a higherdielectric constant could be provided for example by a layer of epoxy orother polymer filled with a material such as any of a variety of wellknown ceramics (not otherwise shown).

The PCB also includes another conductive layer or signal plane 28 andadditional layers 30, 32 and 34 arranged on opposite sides of both thecapacitive laminate 20 and the signal plane 28 to complete the PCB.

The PCB 10 is described only for purposes of example. The inventioncontemplates any of a variety of PCBs having any number of layers. Aswill be apparent from the following description, the invention alsocontemplates other devices or components in addition to the surfacemounted devices 12, 14 and 16 which could be similarly interconnectedwith resistor bodies according to the present invention as described ingreater detail below.

The surface devices 12, 14 and 16 are respectively interconnected withresistor assemblies 36A, 36B and 36C, which could be replaced by othercircuit components according to the present invention. The resistorassemblies are similarly configured but arranged in different conductivelayers or planes of the PCB 10 as described in greater detail below.

The surface mounted device 12 is mounted on the surface 18 of the PCB 10for example by mounting pads 38 and 40 which are respectivelyinterconnected with signal traces 42 and 44.

The signal traces 42 and 44 are respectively interconnected withadditional pads 46 and 48 respectively interconnected with platedthrough-holes 50 and 52.

Referring also to FIG. 2, the resistor assembly 36A surrounds and isconductively interconnected with the through-hole 50 while also beinginterconnected with the conductive or ground plane 24 of the capacitivelaminate 20.

The other plated through-hole 52 can be interconnected with any portionor component of the PCB 10 depending upon the desired operation for thesurface mounted device 12. Similar through-hole interconnections areprovided for the surface mounted devices 14 and 16. Accordingly, thecorresponding components of the surface mounting connections for thosedevices are indicated respectively by primed numerals and double-primednumerals otherwise corresponding to the through-hole connectionsdescribed above for the surface mounted device 12.

Referring particularly to FIG. 3, the resistor assembly 36B is similarlyconstructed as the resistor assembly 36A illustrated in FIG. 2 but isinterconnected with the conductive foil or power plane 22.

Similarly, referring particularly to FIG. 4, the resistor assembly 36Cis also similarly constructed as the resistor assembly 36A while beingarranged in conductive relation with the additional signal plane 28.

As illustrated in FIGS. 1-4, a resistor or circuit component assemblyconstructed according to the present invention may be arranged at theintersection of any through-hole with any conductive plane or layer orcombination thereof in a PCB or the like. FIGS. 2 and 3 specificallyillustrate resistor assemblies interconnected with either the power orground planes 22 and 24 of a capacitive laminate. It will further beapparent from FIGS. 2 and 3 in combination with FIG. 1 that the surfacedevices 12 and 14 could thus be interconnected with both the respectiveresistor or other circuit component assemblies as well as the capacitivelaminate by means of the same respective through-holes.

FIG. 4 illustrates that the resistor or circuit component assembly couldbe arranged in other conductive layers of the PCB. It is also to beunderstood that those conductive layers could even be formed on one ofthe lateral surfaces of the PCB.

Furthermore, the resistor assemblies 36A, 36B and 36C of FIGS. 2-4 aregenerally illustrated at the intersection of through-holes formed in thePCB 10 for other purposes. More specifically, the through-holesillustrated in FIGS. 2-4 are generally contemplated for providingnecessary electrical connections for the respective surface devices withvarious components within the PCB. In that case, the resistor assemblies36A, 36B and 36C are merely added at the juncture of those preexistingthrough-holes with selected conductive layers in the PCB.

At the same time, it is to be understood that a resistor or circuitcomponent assembly constructed according to the present invention couldsimilarly be provided at the intersection of a through-hole and aconductive plane, such a through-hole specifically being provided forpurposes of connection with the assembly. In other words, the resistoror circuit component assembly of the present invention is not to belimited to use with through-holes pre-existing in the PCB for otherpurposes.

In one embodiment of the present invention, the assembly 36A ispreferably formed from a conductive/resistive material exhibiting adesired resistance.

The construction of the resistor circuit component assembly 36A isillustrated in greater detail in FIGS. 5A and 6. Here again, it is to beunderstood that the configuration of the assemblies 36B and 36C issimilar to that described below for resistor circuit component assembly36A.

Referring now to FIGS. 5A and 6, the capacitive laminate 20 isillustrated as a component for inclusion in the PCB 10 of FIGS. 1-4. Forthat purpose, the conductive foils or power and ground planes 22 and 24are initially laminated to the dielectric layer 26 in order to form thecapacitive laminate 20 as a structurally self-supporting component.

In the capacitive laminate 20, the resistor circuit component assembly36A is formed on the upper conductive foil or power plane 22. As notedabove, the method of formation for the resistor circuit componentassembly is particularly simple. At the same time, the method offormation for the resistor circuit component assembly of the inventionmakes it particularly easy to change the effective resistance for eachresistor assembly as described in greater detail below.

Initially, an annular recess 54 is formed in the conductive foil orpower plane 22 between an outer periphery 56 and an inner periphery 58.In addition, since the conductive foil 22 was originally in conductiverelation with the through-hole 50, formation of the annular recess 54also forms a conductive pad 60 between the inner periphery 58 and theplated through-hole 50.

Since the power plane 22 is formed from conductive material, it is thusa simple matter to etch the annular recess 54 at the same time thatother circuit elements are etched into the conductive foil 22 as isconventional for a capacitive laminate in such a PCB.

A resistor body 62 is then arranged or formed in the annular recess 54so that it is electrically interconnected with the power plane, 22 andthe conductive pad 60 at the outer and inner peripheries 56 and 58respectively.

Preferably, the annular recess 54 is formed with its outer and innerperipheries 56 and 58 having constant radii and the conductive pad 60having a similar thickness as the power plane 22, at least adjacent theinner and outer peripheries 58 and 56.

These features particularly simplify predetermination or calculation ofthe total resistance for the resistor body 62 from the respective radiifor the outer and inner peripheries 56 and 58, the thickness of thepower plane 22 (and accordingly the conductive pad 60) and theresistivity of material from which the resistor body 62 is formed. It isassumed that the thickness of the resistor body 62 is approximatelyequal to the thickness of the power plane 22 and the conductive pad 60.

FIG. 5B is provided to illustrate a simplified manner of calculation fordetermining the resistance of the resistor body 62 as described ingreater detail below.

At least in a preferred embodiment of the present invention with theouter and inner peripheries of the resistor circuit component orresistor circuit component assembly having constant radii, the effectiveresistance of the resistor or resistor assembly may be determined asfollows, having reference to FIG. 5B.

If R equals resistance, then it is well known that resistance may becalculated as ##EQU12## where R equals resistance in ohms, p equalsresistivity of the resistor in ohms centimeters, L equals the length ofthe resistor in centimeters, w equals the width of the resistor incentimeters and H equals the height of the resistor in centimeters (wHthus being the effective cross-sectional area of the resistor forpurposes of calculating its resistance).

Referring now to FIG. 5B, the resistor body 62 is graphicallyillustrated with substantially constant radii forming its outer andinner peripheries 56 and 58. Further, since the resistor body 62 forms aresistor between the conductive pad 60 and the conductive layer or uppersurface 22, then the effective length of the resistor body 62 is equalto the radial dimension of the resistor body, that is r₂ -r₁. Theeffective width of the resistor body is thus the mean circumference ofthe resistor body, that is the circumference of the resistor bodygenerated from a point mid-way between the outer and inner peripheries56 and 58. Thus, the effective width of the resistor body may be statedas follows: ##EQU13##

These effective values for length and width may then be substituted intothe basic equation set forth above for resistance. It may readily beseen from FIG. 5B that the overall resistance of the resistor body willbe proportional to the differential radius, that is r₂ -r₁. At the sametime, resistance is inversely proportional to the effective width of theresistor body as stated above.

The above equations can readily be employed for adjusting the radii ofthe outer and inner peripheries of the resistor body in order to provideany desired resistance, at least given the effective height (H) for theresistor body. It is also possible of course to permit variation of theeffective height of the resistor body for purposes of determiningoverall resistance.

Referring briefly to FIG. 5C, in another version of the preferredembodiment of the annular circuit component assembly of the presentinvention, it is illustrated that the inner periphery 58'" of an annularcircuit component 36D can be defined by the outer perimeter of thethrough-hole 50'" However, in this embodiment, the thickness (h) of thepower plane 22 may also be used to determine the effective height (H) ofthe circuit component body 62 for purposes of the above calculations.

The equations set forth above thus readily facilitate the calculation ofresistance relative to dimensions for a preferred embodiment of theresistor body as illustrated in FIG. 5B. At the same time, variations inthe configuration of the resistor body may similarly be included in suchmathematical determinations, but possibly with increased complexityrelative to the equations set forth above.

In this regard, a more precise calculation of the resistance of anannular ring resistor circuit component assembly 62 such as thatillustrated in FIG. 5B may be determined as follows, having reference toFIGS. 5B, 5C and 5D.

Initially, having reference to FIG. 5D, the resistance (R) of a materialbetween points a and b (of any material shape) can be expressed inmicroscopic terms by the following relationship where (V) equalsvoltage, (i) equals current, (E) equals electric field, (j) equalscurrent density and (ρ) equals scalar quantity resistivity: ##EQU14##

In this expression, the line integral d1 defines the line ab along thepath E, and a closed loop path (perpendicular to the direction ofcurrent flow) is defined by the surface integral dS, which correspondsto the area enclosed by a current (i).

The above expression for a rectangular resistor body with dimensions (h,w, I), as shown in FIG. 5D, upon integration readily yields themacroscopic quantity which states that the resistance is directlyproportional to its length and indirectly proportional to itscross-sectional area, ##EQU15##

A model of an annular resistor body 62 is shown in FIG. 5B. The modelhas been simplified in that the resistor body 62 does not overlap thetop of the conductor power plane 22. Overlapping the conductor planereduces the resistance of the resistor per unit volume by exposing moreresistor contact area to the copper foil. If overlap cannot be avoided,the expression can be modified to account for overlap as shown byequation (7) below. Furthermore, the model of the annular resistor body62 has been also simplified in that the effective height (h) of theresistor body 62 may be simply determined from the thickness of thepower plane 22.

Referring still to FIG. 5B, an annular resistor body 62 is illustratedwith substantially constant radii forming its outer and innerperipheries 56 and 58. The resistance value of the annular geometry canonly be approximated and is not accurately described by the aboveexpression relating to the rectangular resistor geometry. Thecross-sectional area of the annular resistor 62 is a continuously andsmoothly changing function of the radii. This functionality is describedby the logarithmic ratio of the outer to inner ring diameter, r₂ and r₁respectively. Assuming that the radial symmetry between the innercontact pad 60 and the annular resistor body 62 is controlled andmaintained during processing, then, the resistance of the annularresistor geometry is exactly expressed as: ##EQU16##

Further, if overlap cannot be avoided, the above expression can bemodified as follows: ##EQU17##

In this expression, d₂ /d₁ describes the ratio of the outer to innerdiameters (not otherwise shown).

The equations set forth above thus provide for the exact calculation ofthe resistance of an annular resistor circuit component formed by theteaching of the present invention, either with or without processingoverlap of the resistor body.

It may also be seen from the method of forming the resistor body 62 thatits effective resistance may be predetermined simply by selecting theappropriate radii for the outer and inner peripheries 56 and 58. Inother words, given the effective thickness of the resistor body and theresistivity of the material from which it is formed, the radii for theperipheries of the resistor body could then be selected in order toestablish its effective resistance.

The resistor body is preferably formed from a liquid precursor such as apowdered resistor material suspended in a liquid. In this manner, theresistor body could be deposited and formed by conventional techniquesif necessary or desired. However, it is to be understood that theresistor body could also be formed from other precursors either inliquid or paste or of other consistencies, even a dry film, for example,

Generally any liquid precursor may be employed for forming the resistorbody-as long as the precursor is capable of being filled or otherwisecombined with a suitable resistor material either in the form of apowder or possibly larger particles. The precursor must also be selectedso that it is capable of withstanding conventional PCB processing steps.

A particular liquid precursor suitable for use in the present inventionmay be taken for example from U.S. Pat. No. 4,870,746 issued Oct. 3,1989 to Klaser under assignment to Litton Systems, Inc. The conductiveor resistive inks described in that reference may also be used forforming the resistor body of the present invention. It is further to benoted that such conductive or resistive inks may be formed either asliquids capable of deposition by suitable silkscreen techniques as apaste suitable for extrusion or planing to form the resistor body.Referring again to FIG. 5A, for example, such techniques areparticularly adapted for forming the resistor body 62 in an annularrecess such as that indicated at 54.

For purposes of the present disclosure, the above noted patent isincorporated herein by reference as though set forth in its entirety.

As noted above, the term "annular recess" is employed in a broadestsense to include other than simple round configurations. Referring forexample to FIG. 7, a circuit component assembly 36E could be formed as areplacement for any of the circuit component assemblies 36A, 36B or 36C.As illustrated in FIG. 7, the circuit component assembly 36E is formedwith an annular recess 64 formed between an inner periphery 66 providedby a plated through-hole 68 and an outer periphery 70 adjacent aconductive plane 72. However, in the configuration of FIG. 7, the outerperiphery 70 is rectangular.

At the same time, a circuit component body 74 is formed by similarsegments 74A-D arranged in conductive interconnection with both theinner and outer peripheries 66 and 70.

Thus, FIG. 7 illustrates that a circuit component assembly can be formedaccording to the present invention with different configurations (ordifferent geometric shapes forming the outer and inner peripheries) forthe annular recess. The inner periphery of the recess can actually beformed by the plated through-hole itself as illustrated in FIG. 7.Design variations such as those illustrated in FIG. 7 may be desirablefor employing the circuit component assembly of the present invention indifferent applications.

It is noted that the above discussion regarding the formation of theannular resistor circuit component assembly 36A or annular resistor body62 is applicable to the formation of any of the annular circuitcomponents of the present invention. In this regard, an annularconductor circuit component may be formed in the same manner as thatabove where the precursor material exhibits low resistivity (higherconductivity). Similarly, an annular inductor circuit component may beformed as above where the precursor material exhibits inductiveproperties such as with a ferro-magnetic precursor material arranged ina suitable matrix. Further, a dielectric/capacitive annular circuitcomponent may be formed by employing a suitable dielectric material, asdescribed below.

In another preferred embodiment of the present invention, it iscontemplated to provide an annular inductor circuit component coupledwith a PCB through-hole. It is further contemplated by the presentinvention that the annular inductor or inductor assembly have outer andinner peripheries with substantially constant radii where the inductanceof the inductor or inductor assembly may be determined as follows.

Initially, just as with the annular resistor body 62 of FIG. 5B, thecross-sectional area of the annular inductor is a continuously andsmoothly changing function of the radii. This functionality is describedby the logarithmic ratio of the outer to inner diameters. Assuming thatthe radial symmetry between the inner periphery of the inductor body andthe contact pad or conductive plated through-hole is controlled andmaintained during processing then, the functional relationship for theannular inductor body may be expressed by the following:

Let:

μ=permeability (H m⁻¹) of the ferromagnetic core

h=thickness of the ferromagnetic core

and the inductance (L) per unit length for an annular core inductorhaving an inner radius of r₁ and an outer radius of r₂ may be determinedin the following manner: ##EQU18##

The above equation can readily be employed for adjusting the radii ofthe outer and inner peripheries of the annular ring inductor body inorder to provide a desired inductance, at least given the effectiveheight (h) for the inductor body. It is also possible of course topermit variation of the effective height of the inductor body forpurposes of determining overall inductance.

The equation set forth above thus readily facilitates the calculation ofinductance relative to dimensions for a preferred embodiment of theinductor body with the same structure as that illustrated by the annularresistor body 62 of FIG. 5B. At the same time, variations in theconfiguration of the inductor body may similarly be included in themathematical determination, but possibly with increased complexityrelative to the equation set forth above.

Either the annular resistor body 62 (more broadly a conductor/resistor)or the annular inductor circuit component described above may also bereplaced by an annular dielectric/capacitor formed as also describedabove wherein the liquid precursor includes material exhibitingdielectric properties such as epoxy or, for example, ceramic particlespreferably having a high dielectric constant. As noted above, such acomponent can function either as a dielectric (isolator) or capacitordepending particularly upon the dielectric constant for the resultingannular dielectric/capacitive annular circuit component.

In this regard, the capacitance (C) per unit length for an annularcapacitor assembly of the present invention formed with substantiallyconstant radii and having an inner radius of r₁, an outer radius of r₂,and an effective thickness (h) may be determined by the followingequation: ##EQU19## ε being defined as follows: ##EQU20## where ε_(r) isthe relative permutivity of the annular medium.

It is further contemplated by the present invention to provide compoundcircuit components (or networks) formed from operative combinations ofpassive circuit components such as conductor/resistors, inductors anddielectric/capacitors.

In one preferred embodiment it is specifically contemplated to formcompound circuit component assemblies within an annular recess ininternal or external layers of a PCB where an annular passive circuitcomponent is arranged within a different annular circuit component toform a series of operatively interconnected concentric circuit componentbodies as illustrated by FIG. 8. In this regard, the term concentric isemployed to mean a plurality of circuit component bodies having a commonaxis where those bodies may be of a variety of geometric shapes.

Referring to FIG. 8, the compound circuit component assembly 80 isformed within the annular recess 92 in a conductive plane 94 of alaminate in a PCB (not otherwise shown). An annular dielectric body 82is formed with its outer periphery 86 in operative contact with theconductive plane 94 and having a constant radius r₃. The inner periphery88 of the dielectric body 82 has a constant radius r₂ and is generallyco-extensive and in operative contact with the outer periphery 96 of anannular inductor body 84. The inductor body 84 may be formed, forexample, from a ferro-magnetic material arranged in a suitable matrix.The outer periphery 96 of the annular inductor body 84 has a constantradius which is substantially equal to r₂. The inner periphery 90 of theinductor body 84 has a constant radius r₁ and is generally co-extensiveand in operative contact with the conductively plated through-hole 98 inthe PCB (not otherwise shown).

In the annular compound circuit component assembly 80 illustrated inFIG. 8 the dielectric body 82 is employed to provide conductiveisolation from the conductive layer 94 in the PCB laminate. In thisregard, the dielectric body 82 may be formed, for example, from asuitable dielectric material having a sufficiently low dielectric value.

Other compound circuit component assemblies may be formed under thepresent invention in same manner as discussed above where the particularcircuit components are varied to provide a desired compound circuit (ornetwork). A process of forming a compound circuit component assemblysuch as that indicated as 80 in FIG. 8 will be act forth below.

Several possible compound circuits formed by the present invention areillustrated in the equivalent circuit diagrams included as FIGS. 9A, 9B,10A, 10B, 11A, 11B, 12A and 12B.

Initially, FIGS. 9A and 9B illustrate High Pass Filter assemblies formedrespectively with an inductor L and capacitor C or a resistor R andcapacitor C' for the purpose of restricting relatively low frequencysignals while allowing relatively high frequency signals to be passedthrough the circuit. In each of the circuit arrays of FIGS. 9A and 9B,the capacitor may preferably be formed by a capacitor laminate formed bymultiple layers of a PCB, the inductor or resistor being generallycoupled with the capacitor to form the equivalent circuits 100 and 110illustrated in those figures.

FIGS. 10A and 10B similarly illustrate Low Pass Filter assembliesformed, for example, from components similar to those described above inconnection with the equivalent circuits of FIGS. 9A and 9B. However, infie equivalent circuits 120 and 130 of FIGS. 10A and 10B, the componentsare interconnected in the manner generally illustrated in the figures inorder to filter or restrict relatively high frequency signals whileallowing relatively low frequency signals to be passed through fiecircuit. It is also noted fiat, in all of the equivalent circuits ofFIG. 9A, 9B, 10A and 10B, the capacitor serves a particular function ofestablishing the level of separation for relatively high and lowfrequency signals.

FIGS. 11A and 11B are similarly equivalent circuits of pi Filters. Hereagain, the equivalent circuits 140 and 150 of FIGS. 11A and 11B arerelatively similar to the equivalent circuits of FIGS. 10A and 10B butwith capacitors coupled on opposite sides of the respective inductor orresistor and interconnected in parallel to ground in order to accomplishthe intended function.

FIGS. 12A and 12B illustrate equivalent circuits 160 and 170 for BandPass Filters wherein a resistor provides the signal communication, forexample, through a PCB, one side of the resistor being coupled to groundrespectively through either a parallel or series arrangement of aninductor and capacitor as illustrated to accomplish the intendedfunction.

Methods of forming the circuit component assembly or circuit componentbody of the present invention are believed clearly apparent from thepreceding description of the invention. However, methods of formationare described below in order to assure a complete understanding of theinvention.

Initially, referring for example to FIGS. 5A and 6, an annular recess isformed in a conductive plane, the annular recess having an outerperiphery and an inner periphery such as those described above.Preferably, the inner periphery also defines a conductive pad. Athrough-hole may be formed axially within the conductive pad eitherprior to formation of the annular recess or after formation of theresistor body and even following its inclusion in a PCB such as thatindicated at 10 in FIGS. 1-4.

Returning to the specific method, the resistor body is then formed inthe annular recess. Preferably, the resistor body is at leastco-extensive with the annular recess and preferably overlaps the outerand inner peripheries while at the same time being at least as thick asthe conductive plane from which the annular recess was formed. Asdescribed above, this particularly simplifies determination of theeffective resistance for the resistor body. With the resistor assemblythus being formed, the conductive plane including the resistor assemblyis then laminated into the PCB or similar circuit board assembly asdescribed above. As was also noted above, the necessary through-holescould be formed following completion of the PCB.

A preferred process for screening materials in the form of a liquidprecursor into an annulus formed in a conductive layer of a PCB may becarried out as described below with reference to FIGS. 14-20 and FIGS.17A, 18A, 17B and 18B considered in combination with FIGS. 14-20. Inthat regard, FIGS. 14-20 contemplate formation of a single circuitcomponent in the annular space while FIGS. 17A-18B, taken together withFIGS. 14-20, illustrate a variation of the process for depositingmultiple components in the annular recess.

Referring initially to FIGS. 14-20, a disposable contact layer 206,preferably formed as a dry film image by silkscreening of a suitablephotoimaging polymer such as an epoxy (or, for example, polymersemployed as soldermask), is imaged onto a conductive layer 202 of alaminate 200, for example, in a PCB (not otherwise shown). Preferably,the conductive layer 202 may be a copper foil laminated to a suitableglass or epoxy layer or substrate 204 as illustrated in FIGS. 14 and 15.

Referring particularly to FIG. 15, the disposable contact layer 206 isapplied to the conductive layer 202 of the laminate 200 to provide agenerally continuous protective layer with a selected area or areas 208exposing or leaving unprotected the underlying conductive layer or film202.

Referring particularly to FIG. 16, a subtractive step such as copperetching is then carried out whereby the exposed area or portion 208 (seeFIG. 15) of the conductive layer 202 is removed from the laminate 200 toform an annular recess 212 (see FIG. 16) in the conductive layer 202' ofthe laminate 200'. Preferably, the exposed area 208 is in an annularconfiguration surrounded by a generally continuous portion 206A of thecontact layer with a central island 206B. The surrounding portion 206Aand the central portion 206B thus respectively define outer and innerperipheries 212A and 212B for the annular recess 212.

Referring particularly to FIG. 17, a screen or stencil 214 is thenarranged above the disposable contact layer 206, the screen or stencil214 having an opening or openings 216 corresponding to the annularrecess 212 in the conductive layer 202'. The screen or stencil 214 maybe a conventional silk, polyester or steel mesh screen, for example, asis well known in the art of PCB manufacture and elsewhere.

Following arrangement of the screen 214 as described above, andcontinuing to refer particularly to FIG. 17, a precursor 218 for thedesired circuit component is then applied through the stencil or screen214 in order to fill the annular recess 212 in the conductive layer 202'and thus form the circuit component as an annular body also illustratedat 218. In this regard, the precursor 218 is preferably a liquidprecursor or ink formed for example from a polymer system such as epoxyto provide a carrier for a suitable material forming the desired circuitcomponent. In this regard, with the desired circuit component beingeither a resistor or conductor, a suitable conductive material such as aconductive polymer or particulate metal having desired characteristicsof resistance and conductance is dispersed within the liquid precursor.In the case of an inductor, a suitable magnetic material such asparticulate ferrite is dispersed within the liquid precursor material.Similarly, either a dielectric or capacitor may be formed by dispersinga suitable material such as a ceramic having a desired dielectricconstant in the liquid precursor. Here again, the circuit componentfunctions as a dielectric or capacitor primarily depending upon thedielectric constant formed for the circuit component. Furthermore, inthe case of a capacitor, it is necessary to provide a conductor at boththe outer and inner peripheries 212A and 212B of the annular recess 212.This function is of course performed by the surrounding portion 202A andthe central portion 202B of the conductive layer 202' as bestillustrated in FIG. 16.

Following formation of the circuit component in the annular recess 212,the screen or stencil 214 is then removed and the precursor material isprebaked in order to at least partially cure the precursor material inan step represented by FIG. 18.

After the prebaking step described above, the disposable contact layer206 is removed or stripped from the laminate 200' in order to expose apartially cured circuit component 220. The laminate 200' may then besubjected to a final cure step represented by FIG. 20 in order tocomplete curing of the annular circuit component 220 so that it ispreferably generally coplanar with the surrounding portions 202A of theconductive layer 202' as illustrated in FIG. 20.

Thus, there has been described above a process for forming an annularcircuit component which may be either a resistor/conductor, an inductoror a dielectric/capacitor in a layer of a laminate or PCB.

The present invention further contemplates a variation of the processdescribed above in order to form multiple components in the annularrecess 212. Such a process may be carried out for example by repetitiveperformance of the steps described above with respect to FIGS. 17 and18. The repetitive steps are illustrated respectively in FIGS. 17A, 18A,17B and 18B and are described below in order to assure a completeunderstanding of the invention.

Following performance of the same steps described above with referenceto FIGS. 14-16, the screen or stencil 214A is preferably formed toexpose only an inner concentric portion 212C of the annular space 212'.A precursor for a first circuit component 220C is then deposited in theexposed portion of the annular recess 212' to form the component 220C.

The screen 214A is then removed as illustrated in FIG. 18A and replacedby a second screen 214B as illustrated in FIG. 17B exposing an outerconcentric portion 212D of the annular recess 212'. A separate precursormaterial is then applied through the screen 214B in order to form asecond circuit component 220D in an outer concentric portion of theannular recess 212'. Thus, the annular recess 212' is filled with twoconcentric circuit components 220C and 220D as described above.

Thereafter, the second screen 214B may be removed as illustrated in FIG.18B and the remaining steps of the process carried out as describedabove with reference to FIGS. 14-20,

Some variations may be desirable in the alternate method for formingcompound circuit components. For example, it may be desirable to prebakeor otherwise treat the precursor for the initially deposited component220C in order to assure that it fills only the desired inner concentricportion of the annular recess 212'. After deposition of the secondcircuit component 220D to completely fill the annular space 212',further curing may be carried out in a generally similar manner asdescribed above with reference to FIGS. 14-20 in order to completeformation of the compound circuit components 220C and 220D.

The specific functions of the circuit components 220C and 220D may ofcourse be determined by the use of suitable materials dispersed withinthe liquid precursor as described above for either a resistor/conductor,inductor or dielectric/capacitor, for example.

The compound method described immediately above could of course befurther varied in order to form additional circuit components in acompound configuration. Furthermore, the alternate compound method couldalso be varied in order to form separate circuit components in otherthan the concentric relation described above. For example, radialsegments of the annular region 212' could be respectively exposed andfilled during the process in order to form suitable circuit components,if desired, which would then be in generally parallel interconnectionbetween the conductive elements provided by the outer portion 202A' andinner portion 202B' of the conductive layer 202'.

It is further contemplated that the processes described above may beemployed to form one or more circuit components in an annular recesssurrounding a via or through-hole (not illustrated in FIGS. 14-20). Sucha via or through-hole is illustrated for example in FIGS. 1-4.Accordingly, the processes described above may be further varied byformation of such a via or through-hole, for example, to replace thecentral portion 202B or 202B' of the conductive layer 202 or 202'.

In any event, there have been described above different embodiments of anovel circuit component assembly contemplated for arrangement in anannular recess or at the intersection between a through-hole and aconductive plane in a PCB or the like. There have also been describedmultiple methods for forming such circuit components. Additionalvariations in both the embodiments and processes described above will beapparent from the preceding description. Accordingly, the specific scopeof the invention is defined only by the following claims which arefurther exemplary of the invention.

What is claimed is:
 1. A method of forming a circuit component assemblyin a conductive layer of a printed circuit board (PCB), comprising thesteps of:forming an annular recess in the conductive layer about aconductive element comprising one of (a) a through-hole and (b) acentral conductor in the PCB; forming a circuit component assembly inthe annular recess, the circuit component assembly including at leastone circuit component body and having an outer perimeter interconnectedwith the conductive layer; and operatively interconnecting theconductive element with an inner perimeter of the circuit componentassembly.
 2. The method of claim 1 further comprising the step offorming the outer and inner perimeters of the circuit component assemblywith substantially constant radii and forming the circuit componentassembly to be generally coextensive with the annular recess whereby theouter perimeter of the circuit component assembly is connected with theconductive layer and the inner perimeter of the circuit componentassembly is operatively connected with the central conductive element.3. The method of claim 1 further comprising the step of forming aconductive pad interconnected between the conductive through-hole andthe inner perimeter of the circuit component assembly.
 4. The method ofclaim 3 further comprising the step of forming the outer and innerperimeters of the circuit component assembly with substantially constantradii and forming the circuit component assembly to be generallycoextensive with the annular recess whereby the outer perimeter of thecircuit component assembly is in full register with the conductive layerand the inner perimeter of the circuit component assembly is in fullregister with the conductive pad.
 5. The method of claim 4 furthercomprising the step of forming the conductive layer and conductive padwith generally equal thicknesses at their respective interconnectionswith the circuit component assembly for establishing the effectivethickness of the circuit component assembly.
 6. The method of claim 5further comprising the step of forming the circuit component body from aliquid precursor.
 7. The method of claim 1 wherein the conductive layeris a portion of a capacitive laminate in the PCB.
 8. The method of claim1 further comprising the step of forming the circuit component assemblybody from a liquid precursor.
 9. A method of forming a circuit componentassembly in a conductive layer of a PCB laminate comprising the stepsof:applying a protective layer onto the conductive layer of the laminateto expose an annular portion of the conductive layer; removing theexposed portion of the conductive layer by a subtractive step to form anannular recess in the conductive layer around a conductive centerportion; depositing a liquid precursor into the annular recess; removingthe protective layer from the conductive layer of the laminate; andcuring the liquid precursor to form the annular circuit componentassembly with its outer periphery connected to the conductive layer ofthe laminate and its inner perimeter connected to the conductive centerportion.
 10. The method of claim 9 wherein the liquid precursorcomprises a circuit component material selected from the groupconsisting of conductive/resistive materials, inductive materials anddielectric/capacitive materials.
 11. The method of claim 9 furthercomprising the step of forming a conductive element comprising one of(a) a through-hole, and (b) a central conductor in the conductive centerportion of the circuit component assembly and the underlying laminatestructure whereby the central conductive element is operative connectedwith the inner perimeter of the circuit component assembly wherein theconductive laminate forms a portion of a CB.
 12. The method of claim 9further comprising the step of partially curing the liquid precursorprior to removal of the protective layer.
 13. The method of claim 9further comprising the steps of:arranging a screen or stencil above thedisposable contact layer after the subtractive step has been performed,the screen or stencil having an annular opening therein in register withthe annular recess formed in the conductive layer by the subtractivestep; and depositing the liquid precursor in the annular recess of theconductive layer of the laminate through the corresponding annularopening or openings in the screen or stencil.
 14. The method of claim 12wherein the circuit component material is selected from the groupconsisting of conductive/resistive materials, inductive materials anddielectric/capacitive materials.
 15. The method of claim 13 furthercomprising the step of partially curing the liquid precursor prior toremoval of the protective layer.
 16. The method of claim 9 for forming acompound circuit component assembly and further comprising the stepsof:arranging a first screen or stencil above the disposable contactlayer after the subtractive step has been performed, the first screen orstencil having an annular opening therein in register with a firstportion of the annular recess formed in the conductive layer by thesubtractive step; depositing a first liquid precursor in the firstportion of the annular recess in the conductive layer of the laminatethrough the corresponding annular opening in the first screen orstencil; removing the first screen or stencil; arranging a second screenor stencil above the disposable contact layer, the second screen orstencil having an annular opening therein in register with a secondportion of the annular recess formed in the conductive layer by thesubtractive step; and depositing a second liquid precursor in the secondportion of the annular recess in the conductive layer of the laminatethrough the corresponding annular opening in the second screen orstencil.
 17. The method of claim 16 wherein the first and second liquidprecursors comprise materials selected from the group consisting ofconductive/resistive materials, inductive materials,dielectric/capacitive materials and combinations thereof.